I have a 2 year old Fuji S2 that I bought new with a couple of Tamron lenses and I need some advice choosing the right lens to take portraits and full body glamour shots. I know the lens makes the camera and how important the lens is but I am having a hard time justifying the difference of cost. Is the Nikor that much better. I like the 18-50mm for flexibility. All comments would be appreciated.

None of those lenses works as a headshot lens. If you're serious about headshots, then get an 85mm prime lens. I use a 105 - but that's just my preference.

I'd also observe that if you're shooting "full body" shots - you don't need a wide angle lens, you need a bigger studio. Wide angle can easily cause some distortion which is likely not to be too flattering. Particularly in glamour.

As an aside, I'd like to have that Sigma 18-50 for confined space work.

As Mr. Warren pointed out, the wider the angle (and the closer you get to the subject), the more likely it is that you'll get some "fisheye" distortion, unless you spend some serious $$ on a non-fe wide angle.